The term “ranging” refers to a process of determining the distance from one location to another. There are a variety of systems that are able to determine distance, such as SONAR (SOund Navigation And Ranging), RADAR (RAdio Detection And Ranging), LIDAR (LIght Detection And Ranging), and LADAR (LAser Detection And Ranging). One type of ranging technique uses travel time measurements to determine distance. For example, a sensor may transmit a sound or light pulse at a target, and measure a time until an echo is reflected off of the target to determine the distance to the object. Other types of ranging techniques use continuous sound or light waves. For example, a sensor may transmit a continuous sound or light wave at a target, and reflections from the target will interfere with the sound or light wave creating an “interference” wave. When the transmitted wave and the reflected wave (of the same frequency) combine to form the interference wave, the resulting pattern of the interference wave is determined by the phase difference between the transmitted wave and the reflected wave. This phase difference can be used to determine the distance to the target.
Ranging sensors such as this may be used in the manufacture or assembly of products, such as aircraft. When parts are being assembled, precise measurements may be needed in order to assure that the parts are assembled correctly. It can be difficult to match shapes and contours of large parts during assembly, especially when they are fabricated at different locations. If laser ranging sensors are used in assembly processes, it is desirable to design the laser ranging sensors to provides measurements with a very high-precision.